subsequent polymerization of monomers from each phase at the interface between the bulk (continuous) phase, and the dispersed droplets. Polyurethanes and polyureas are materials suitable for producing the microcapsules. The microcapsules comprise a polymeric sphere and a liquid centre, ranging from 30 micron to 2 mm in diameter, depending on monomers and solvents used.
Highly viscous and thickened hydrogels have been used to deliver pheromones, fragrances and other non-water soluble actives. U.S. Pat. No. 4,755,377, for example, describes a process of encapsulating perfume or fragrant material within an aqueous-based gel composition. The resulting material is in the form of a highly viscous semi-solid. U.S. Pat. No. 5,645,844 describes the use of chitosan paste for delivery of pheromones to disrupt insect mating, where the material can be dispensed by an apparatus such as a caulking gun. Due to their thickness and high viscosity, these materials, however, are generally unsprayable compositions.
Most hydrogels are safe and non-toxic to humans. Hydrogels are have been used for the encapsulation of biological materials whereby the formulation is non-lethal to the viability of the cells, proteins, and related materials. U.S. Pat. No. 4,689,293, describes the process of encapsulating living tissue or cells in alginate beads. The encapsulation shell permits the passage of materials and oxygen to the cells and permits the diffusion of the metabolic by-products from the gel. In U.S. Pat. No. 5,635,609, the encapsulation art described involves one esterified polysaccharide (i.e., alginate) and one polyamine (i.e. chitosan) whereby the outer surface membranes are formed through covalent amide bonds. U.S. Pat. No. 4,439,488 teaches a process of encapsulating pheromone whereby the biological agents are dissolved or dispersed in an aqueous paste of a gel-forming polyhydroxy polymer. By adding boric acid to an alkaline pH, the paste transforms into a gel thereby entrapping the agents in a protective matrix.
Japanese patent S 60-252403 describes a method of forming sprayable, slow release pheromone agent obtained by emulsification co-polymerization. In Japanese patent H-9-1244-08, the outer surface of the delivery system (i.e., synthetic resin or inorganic substance) is coated by a water-proof material. The water-proof agent can be a silicon, fluroine, or paraffin hydrogen carbide type material.
A method of delivering active material using a plurality of microbeads suspended in solution is provided, where the microbeads comprise a hydrophilic matrix having droplets of active material entrained therein and a secondary layer adjacent to the surface of the matrix. Furthermore, the matrix is capable of immobilizing a broad spectrum of active materials, either water soluble or non-water soluble. In one aspect of the invention, the hydrophilic matrix may be made from a naturally occurring material to provide an environmentally friendly microbead.
In an aspect of the invention, the active entrained in the matrix diffuses through the hydrophilic matrix and the secondary layer, and is released into the environment over an extended period.
In another aspect, the microbeads are capable of re-hydrating after an initial dehydration and release of active. Thus, the release and longevity of the active can be controlled by adjusting the humidity of the environment in which the microbeads have been delivered.